Graphesthesia is the ability to recognize writing on the skin purely by the sensation of touch. Its name derives from Greek graphē ("writing") and aisthēsis ("perception"). Graphesthesia tests combined cortical sensation; therefore, it is necessary that primary sensation be intact bilaterally[1].
During medical or neurological examination graphesthesia is tested in order to test for certain neurological conditions such as; lesions in nerve roots, peripheral nerves, brainstem, spinal cord, sensory cortex or thalamus. An examiner writes single numbers or simple letters on the skin (usually the palm) with something dull like the back of pen, pen light, tongue depressor, etc. Prior to the start of testing, an agreement must be reached between the examiner and the patient as to the orientation of the letters. During testing, the examiner should gently wipe the palm between each drawing to clearly indicate to the patient that a new letter or symbol is being drawn[2].
The patient provides a verbal response identifying the figure which was drawn. If the patient has a speech or language impairment which prevents him from verbalizing an answer, the answer can be selected from a series of images which are shown to him[2]. Most people are able to determine the letters which are being written on the skin. In cases where the patient is unable to correctly identify the letters (agraphesthesia)[1], he/she would be referred to a specialist for further evaluation.
Loss of graphesthesia indicates either parietal lobe damage on the side opposite the hand tested or damage to the dorsal columns pathway at any point between the tested point and the contralateral parietal lobe.
Testing graphesthesia can be substituted for stereognosis if a patient is unable to grasp an object[2].